This relates generally to a trimmable (or adjustable) current reference generator for semiconductor non-volatile memories.
In order to ensure repeatability of memory operations, current references are generally employed having a high degree of stability, in particular with respect to changes of temperature or supply voltage (Vcc).
Known current reference generators envisage the use of a bandgap voltage reference generator coupled to an active element, like a MOS transistor. As is known, bandgap voltage references create a very stable reference voltage with respect to both temperature and power supply variations; this reference voltage is used to drive the active element, which in turn generates a corresponding reference current.
Accordingly, the reference current Iref generated by the current reference generator (whose value can be controlled through the electrical parameters of the output active element) will exhibit substantially the same stability with respect to temperature and power supply variations as the bandgap reference voltage Vref.
However, as is well known in the art, manufacturing processes in the semiconductor industry are subject to stochastic errors, causing a real process to differ from an ideal or target process. In particular, real processes distribute according to a Gaussian pattern around a target process. A key parameter used to characterize manufacturing processes is the switching speed of the resulting electrical components/devices, based on which a given process can be classified according to so called “process corners” (e.g. “fast”, “slow” or “typical” process corners).
In the above described current reference generator, the generated reference current is not invariant with respect to deviations in the manufacturing process (so called “process skews”). As a result, current reference generators having different electrical properties usually result from a same manufacturing process, due to inherent variations in the process parameters among the various manufactured batches (having different process corners).